JP6985668B2 - Control method of optical communication node, optical communication system and optical communication node - Google Patents

Description

The present invention relates to an optical communication system and an optical communication node included in the optical communication system.

In the current optical communication network, a large capacity is realized by using a wavelength division multiplexing (WDM) technology in which optical signals of a plurality of different wavelengths are simultaneously mounted on a single optical fiber cable. An optical communication network using WDM technology connects nodes with different wavelengths and sets an optical communication path for virtually any connection (hereinafter, the optical communication path is referred to as a path). The wavelength configuration used for these paths was operated almost fixedly.

On the other hand, with the development of video-on-demand and social media in recent years, the traffic demand on the Internet has been fluctuating from moment to moment. Optical communication networks are also required to efficiently and flexibly handle such time-varying traffic. For example, it is preferable to be able to flexibly change the capacity of the path between the nodes and the wavelength configuration forming the path in response to changes in traffic demand. However, configuring a new path or changing the communication capacity of an existing path is affected by the configuration of the existing path. For example, it is affected by the start node and end node of the existing path, the wavelength used, the wavelength bandwidth, and the like. Therefore, the wavelength resources in the communication band of optical communication cannot always be used efficiently, and the traffic capacity efficiency of the network cannot be maximized.

FIG. 1 is a diagram illustrating an example of a traffic time change in a conventional optical communication network. FIG. 1 (a) shows a node configuration of an optical communication network, and FIG. 1 (b) conceptually shows a signal on each node or path on the wavelength axis. In FIG. 1A, a traffic from node A to node C is considered in an optical communication network consisting of four nodes, node A, node B, node C, and node D. Now consider the situation where the path is set as follows. Also referring to (b) of FIG. 1, signals 1 to 6 are first added from the Add unit 1 (A: Add) at the node A and transmitted in the node B direction. At the node B, the signal 2 and the signal 4 among the signals 1 to 6 are dropped from the drop unit 2 of the node B (B: Drop). Further, the remaining signals 1, 3, 5, and 6 are dropped (C: Drop) from the Drop unit 3 of the node C. In such a situation, it is assumed that a new traffic demand is generated and it becomes necessary to set the path of the signal 7 from the node B to the node C. The WDM wavelength band from node B to node C has a sufficient margin as a whole. However, since the wavelength band 7 of the signal 7 overlaps the entire band 5 of the signal 3 and a part of the band 6 of the signal 5, the node B cannot accommodate the signal 7. After all, even if the wavelength band as a whole has a vacancy and a margin, the traffic cannot be accepted depending on the mode of the path for new traffic. In order to solve such a problem, for example, Non-Patent Document 1 proposes wavelength defragmentation.

FIG. 2 is a diagram illustrating the concept of wavelength defragmentation in Non-Patent Document 1. Non-Patent Document 1 discloses wavelength defragmentation by three steps in a linear network consisting of nodes A to D as shown in FIG. In Step 1 in the initial state, Signal1 to Signal4 are transmitted between node A and node D. In each step, the vertical direction represents the wavelength λ, and the horizontal axis direction represents the node position (transmission direction). Signal 1 (wideband signal) having a wide bandwidth is transmitted between nodes A and C, and Signal 4 (narrow band signal) having a narrow bandwidth is transmitted between nodes A to B. The state of Step 2 is a state in which Signal 3 in which a path is set from node C to node D in Step 1 in the initial state is abolished. Here, the wavelengths of Signal2 (10a) and Signal1 (9a) can be gradually changed downward (for example, on the short wavelength side). As a result, in Step 3, an empty wavelength band 8 can be provided in the wavelength band originally occupied by Signal 1, and the traffic accommodation efficiency in the wavelength resource can be maximized. Non-Patent Document 1 discloses an example of successful transmission of a 100 G double polarized wave 4-phase shift keying (DP-QPSK) signal.

Kyosuke Sone, Xi Wang, Shoichiro Oda, Goji Nakagawa, Yasuhiko Aoki, Inwoong Kim, Paparao Palacharla, Takeshi Hoshida, Motoyoshi Sekiya, and Jens C. Rasmussen, “First Demonstration of Hitless Spectrum Defragmentation using Real-time Coherent Receivers in Flexible Grid Optical Networks, ”ECOC2012, _Th.3.D.1 (PD) Hideto Yamamoto, Kohei Saito, Akira Naga, Hideki Maeda "Realization of Uninterrupted Wavelength Defragmentation for Flexible Optical Networks by Wavelength Diversity Transmission Using Maximum Ratio Synthesis", 2015, 2015 Institute of Electronics, Information and Communication Engineers Society Conference, B -10-66

However, the wavelength defragmentation disclosed in Non-Patent Document 1 has a problem that the control for carrying out the defragmentation is complicated and troublesome. According to the method of Non-Patent Document 1, it is necessary to change the wavelength of the optical signal on the transmitting node side and the wavelength of the locally oscillated light for the receiver on the receiving node side in synchronization between these nodes at remote locations. There is. Further, it is necessary to synchronously change the wavelength of the transmission band used by the wavelength selection switch at the node through which the optical signal passes.

FIG. 3 is a diagram illustrating an outline of a control operation required for each node in the wavelength defragmentation of the prior art. FIG. 3 shows control when the wavelength of the optical signal is switched in synchronization between the node A11, the node B12, and the node C13. It is assumed that a signal is input from the ad circuit 14 of the node A11 to transmit an optical signal having a wavelength λ1 and the signal is output from the drop circuit 15 of the node C13 via the node B12. Consider a case where the wavelength used here is switched from λ1 to λ2 and the wavelength is rearranged. At this time, the Tx frequency (wavelength) of the transmitter 16 for the signal at the node A11, the transmission wavelength of the plurality of wavelength selection switches of the nodes A to C, and the frequency (wavelength) of the local oscillator for the receiver of the node C13. ) Need to be controlled synchronously. Therefore, when rearranging the wavelength from λ1 to λ2, complicated control of the optical transmission device is required over three remote nodes.

In addition, due to the difference in wavelength bandwidth, wavelength rearrangement in which wavelengths intersect, for example, wavelength rearrangement in which the relationship between Signal 1 and Signal 4 in FIG. 2 is exchanged, could not be performed. The optical transmission equipment arranged in the node often uses a laser light source. When changing the wavelength of the laser light source, it is not possible to change the wavelength digitally instantaneously, and it is necessary to change the resonance length of the laser in an analog manner to stabilize the oscillated light.

In many optical transmission devices, it takes a certain amount of time to change the wavelength for communication to a state in which it can actually be used. From the user's point of view, the optical signal will be completely stopped at the time of switching, and communication will be interrupted. If the other signal in the band between the two wavelengths to be switched contains the wavelength in use, the signal in use may be disturbed or communication may be interrupted while the wavelength is switched. After all, changing the wavelength during actual optical communication network operation is troublesome and requires complicated control, there is a limit to the range that can be changed, and it is not possible to switch wavelengths without interrupting service or degrading communication quality. was difficult.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a mechanism of wavelength defragmentation that is more flexible and simpler than that of the prior art.

In order to achieve such an object, the invention according to claim 1 is an optical communication system in which optical signals having different wavelengths are multiplexed to transmit information data, in which wavelengths from different input paths are used. Multiple wavelength selection switches for demultiplexing the divided multiplex signal, and a plurality of combined waves for combining wavelength-divided multiplex signals including the demultiplexed signal light from each of the plurality of demultiplexing wavelength selection switches. The wavelength selection switch and the plurality of paths for interconnecting each of the plurality of demultiplexing wavelength selection switches and each of the plurality of combined wave wavelength selection switches are provided, and the plurality of combined waves are provided. A wavelength conversion means is installed for at least one of the paths connected to the wavelength selection switch, and the first optical signal before the wavelength conversion by the wavelength conversion means and the first light. The second optical signal whose signal has been wavelength-converted is among the plurality of combined wave wavelength selection switches during the phase synchronization procedure between the first optical signal and the second optical signal. The wavelength of the first optical communication node configured to be output simultaneously from one wavelength selection switch for combined waves, the first optical signal from the first optical communication node, and the second optical signal. A wavelength demultiplexing means for demultiplexing, a timing estimation unit for estimating the timing of information data between the first optical signal and the second optical signal, and the first optical signal and the second optical signal. A wavelength switching processing means including a timing adjusting unit for reducing the timing difference of information data between optical signals is provided, and a second optical communication node for dropping the second optical signal carrying the information data is provided. It is an optical communication system characterized by. The above-mentioned first optical communication node is an optical communication node that performs wavelength conversion, and the above-mentioned second optical communication node is an optical communication node at a receiving end.

The invention according to claim 2 is the optical communication system according to claim 1, wherein the timing estimation unit coherently detects and decodes the first optical signal and the second optical signal, respectively. Timing estimation is performed for the two information data, and the timing adjusting unit synthesizes the two information data at the maximum ratio and adjusts the timing of the two information data so as to maximize the combined output. It is characterized by being a maximum ratio synthesizer. The above-mentioned maximum ratio synthesis unit can be, for example, an adaptive MIMO equalization unit in which the coherently detected first optical signal and the second optical signal are input and used in communication technology. ..

The invention according to claim 3 is the optical communication system according to claim 1 or 2, wherein at least one path of the first optical communication node is a demultiplexing wavelength selection switch and the combined wavelength. It is characterized by including a path of at least one combination of selection switches or a path from an Add port connected to the plurality of wavelength selection switches for combined waves.

The invention according to claim 4 is the optical communication system according to any one of claims 1 to 3, further comprising an excitation light generating means for supplying excitation light to the wavelength conversion means, and the wavelength conversion means is used for wavelength conversion. Is an all-optical wavelength conversion means implemented only in the optical layer.

The invention according to claim 5 is the optical communication system according to claim 4, wherein the excitation light generation means is generated by an excitation light generation unit that generates frequency comb light from CW light and the excitation light generation unit. The comb separation means for spatially demultiplexing the frequency comb light into a single CW light for each comb frequency, a plurality of frequency shift units for shifting the frequency of the single demultiplexed CW light, and the above. It is characterized by including an excitation light selective distribution means that combines the frequency-shifted CW light from each of the plurality of frequency shift units and spatially demultiplexes the CW light.

The invention according to claim 6 is the optical communication system according to claim 5, wherein the excitation light selective distribution means is a wavelength selection switch having multiple inputs and multiple outputs.

The invention according to claim 7 performs wavelength conversion on the first optical signal having a wavelength λ1 at the first optical communication node in the optical communication system according to any one of claims 1 to 6. , A step of generating the second optical signal of wavelength λ2, and a step of estimating the timing of the first optical signal and the second optical signal by the timing estimation unit in the second optical communication node. In the step of operating the timing adjusting unit so that the timing difference between the first optical signal and the second optical signal is reduced in the second optical communication node, and in the second optical communication node. The step of switching the reception path from the first optical signal to the second optical signal and acquiring the information data from the second optical signal, the first optical communication node, and the second light. It is a control method of an optical communication node, characterized in that a phase synchronization procedure including a step of deleting an optical path related to λ1 is performed on the communication node.

According to another aspect of the present invention, in an optical communication system that multiplexes optical signals of different wavelengths and transmits information data, the optical communication node that drops the optical signal carrying the information data is different optical communication. from the node, a first optical signal before being wavelength converted, and a pre-Symbol second optical signal the first optical signal is wavelength-converted, and the wavelength demultiplexing unit for wavelength-demultiplexing said first The timing estimation unit that estimates the timing of the information data between the optical signal and the second optical signal, and the timing difference of the information data between the first optical signal and the second optical signal. The different node includes a wavelength switching processing means including a timing adjusting unit for reducing, and the different nodes are a plurality of wavelength division wavelength selection switches for demultiplexing wavelength division multiplex signals from different input routes, and the plurality of wavelength division wavelength selection switches. A plurality of wavelength-dividing wavelength selection switches for merging wavelength-divided multiplex signals including the demultiplexed signal light from each of the switches, and each of the plurality of demultiplexing wavelength selection switches and the plurality of combined waves. The first path has a plurality of paths that are interconnected with each of the wavelength selection switches for wavelength selection, and the first path is for at least one of the paths connected to the plurality of wavelength selection switches for combined waves. is the established wavelength converter for wavelength-converting the optical signal or found before Symbol second optical signal, during the phase synchronization procedure between the first optical signal and the second optical signal, said first The optical communication node is configured so that the optical signal of the above and the second optical signal are simultaneously output from one of the plurality of wavelength selection switches for wavelength selection. It can also be carried out. Here, the optical communication node is a receiving end optical communication node, and the different optical communication node is an optical communication node that performs wavelength conversion.

As described above, the present invention provides a mechanism for wavelength defragmentation that is more flexible and simpler than the prior art.

FIG. 1 is a diagram illustrating a change in traffic time of an optical communication network. FIG. 2 is a diagram illustrating wavelength defragmentation of the prior art. FIG. 3 is a diagram illustrating wavelength defragmentation control according to the prior art. FIG. 4 is a diagram showing a schematic configuration of the optical communication node of the present invention. FIG. 5 is a diagram showing a configuration of a pump light generating means of the optical communication node of the present invention. FIG. 6 is a diagram showing spectra of each part in the pump light generating means. FIG. 7 is a diagram showing the configuration of the wavelength conversion means of the optical communication node of the present invention. FIG. 8 is a diagram illustrating a spectrum of each part in the wavelength conversion means. FIG. 9 is a diagram illustrating an operation of wavelength conversion in which two optical signals are exchanged. FIG. 10 is a diagram showing the configuration and operation of the M × pWSS of the first embodiment. FIG. 11 is a diagram illustrating a configuration of LCOS used in the second embodiment. FIG. 12 is a diagram showing an outline of circuit elements of a space beam converter. FIG. 13 is an optical path diagram of an optical system that integrates the three WSSs of the third embodiment. FIG. 14 is a diagram showing the configuration of the optical communication node of the fourth embodiment. FIG. 15 is a diagram showing the configuration of the optical communication node of the fifth embodiment. FIG. 16 is a diagram showing the configuration of the optical communication system of the sixth embodiment. FIG. 17 is a diagram showing a flow of a phase synchronization procedure at a receiving end node. FIG. 18 is a diagram showing the configuration of the optical communication system of the seventh embodiment.

The optical communication node of the present invention provides a novel configuration for wavelength defragmentation. At least one wavelength conversion means is provided in the middle of the path between the input port (WSS and Add port for demultiplexing for route switching) and the output port (WSS for combined wave) in the communication node. Of the paths from one input port to the output ports towards multiple directions, some are direct connections and wavelength conversion means are provided on some of the remaining paths. Wavelength conversion means may be provided in all paths. For the wavelength conversion means, the pump light used for wavelength conversion is supplied from the pump light generating means. Efficient and integration-friendly configurations for supplying pump light to the wavelength conversion means are also disclosed.

Further, an optical communication system in which a wavelength defragmentation operation in an optical communication node that switches wavelengths and a phase synchronization procedure of two optical signals having different wavelengths in a receiving end node that drops information data are linked, and a control method for these optical communication nodes. Will also be disclosed. Hereinafter, the overall configuration of the optical communication node of the present invention, its operation, and the specific configuration of each component will be described in detail with reference to the drawings.
[Optical communication node configuration]
FIG. 4 is a diagram showing a schematic configuration of the optical communication subsystem of the present invention. The optical communication subsystem 20 of FIG. 4 corresponds to the node B and the node D having the number of directions N = 3 in FIG. 1. Typically, the optical communication subsystem 20 corresponds to an optical communication node in, for example, a ROADM (Reconfigurable Optical Add / Drop Multiplexer) system. Hereinafter, for the sake of simplicity, the optical communication subsystem 20 of FIG. 4 will be referred to as an optical communication node. The optical communication node of FIG. 4 has a configuration in which a functional block required for wavelength defragmentation according to the present invention is added in addition to the configuration of a general optical communication node of the prior art. The optical communication node 20 of FIG. 4 shows an example of the configuration of an optical network node having the number of directions N = 3, but the number of directions N is not limited to 3, and can be configured in a scalable manner by adapting to different numbers of directions N. ..

In FIG. 4, the wavelength division multiplexing signals (hereinafter referred to as WDM signals) from the inputs (In1, In2, In3) of different directions are the wavelength division multiplexing signals 21-1 to 21-3 (WSS: Wavelength Selective Switch) (WSS: Wavelength Selective Switch) (WSS: Wavelength Selective Switch) (WSS). It is input to Ingress1 to Ingress3). The input WDM signal is wavelength demultiplexed by each of the demultiplexing WSSs 21-1 to 21-3, and is routed to one of the desired directions (Out1 to Out3) for each wavelength. The routed optical signal is wavelength-combined by the corresponding combined wave WSS29-1 to 29-3 (Egress1 to Egress3) in each direction (Out1 to Out3). The optical signal wavelength-multiplexed by the combined wave WSS29-1 to 29-3 is output as a WDM signal from each output (Out1 to Out3) of WSS29-1 to 29-3.

In the routing in the optical communication node 20 described above, the input side demultiplexing WSS21-1 to 21-3 and the output side combined wave WSS29-1 to 29-3 are the paths and the paths shown by the dotted lines in FIG. 4, respectively. It is connected by the path shown by the solid line. Here, a path between WSSs on the same route, such as between In1 and Out1, is meaningless because the signal is routed to the same route and an optical signal is returned. Therefore, in the optical communication node 20, there is no connection between the demultiplexing WSS and the combined WSS in the same direction.

The paths 23-1 to 23-3 shown by the dotted lines in FIG. 4 are paths that directly connect the demultiplexing WSS on the input side and the combined WSS on the output side. On the other hand, the paths (paths) 22-1 to 22-3 shown by the solid line are paths newly added in the optical communication node of the present invention, and the wavelength conversion means is inserted on each path. .. In the conventional optical communication node, the WDM signal input from the route In1 is wavelength-divided via the demultiplexing WSS21-1, and the combined wave WSS29-2 via the dotted path 23-1. Directly connected to 29-3. In the optical communication node 20, when the wavelength is demultiplexed via the demultiplexing WSS21-1 and the wavelength is demultiplexed and the solid line path 22-1 is passed, the wavelength conversion means 24a to 24d are passed through, respectively, and the combined wave WSS29-2, Connected to 29-3. The optical signal demultiplexed by the demultiplexing WSS21-1 is wavelength-converted by the wavelength conversion means 24a to 24d, and then routed to a desired direction via the combined wave WSS29-2 to 29-3. For the path 22-2 from the demultiplexing WSS22-2 to the combined wave WSS29-1 and 29-3, and for the path 22-3 from the demultiplexing WSS22-3 to the combined wave WSS29-1 and 29-2. Also, a similar wavelength conversion means is installed.

Therefore, in the optical communication node of the present invention, each of the plurality of wavelength selection switches 21-1 to 21-3 for demultiplexing and the plurality of wavelength selection switches for demultiplexing that demultiplex the wavelength multiplex signals from different input routes. A plurality of wavelength selection switches 29-1 to 29-3 for combining wavelength multiplex signals including an optical signal demultiplexed from the above, each of the plurality of wavelength selection switches for demultiplexing, and the plurality of wavelength selection switches. At least one of the routes 22-1 to 22-3 connected to the plurality of wavelength selection switches for wave length, which comprises a plurality of paths interconnected with each of the wavelength selection switches for wave combination. It can be carried out assuming that wavelength conversion means are installed for one path. This at least one path is a path of at least one combination of the demultiplexing wavelength selection switch and the combined wave wavelength selection switch.

In a specific connection path (for example, In1 → Out2), q wavelength conversion means are installed. Therefore, q is the number of paths including the wavelength conversion means in a specific connection path. In the configuration example of the optical communication node in FIG. 4, q = 2, and the value of q may be 1 or 3, but the larger the q, the higher the degree of freedom when performing wavelength defragmentation in the optical communication node. In the optical communication node 20, the value of q may be different for each connection path (routing route) for the WSS for demultiplexing one route. Further, for some other reason, a part of the optical communication node 20 may include a route in which q = 0, that is, a wavelength conversion means is not installed.

The simplest configuration, as shown in FIG. 4, includes the same number of paths with wavelength conversion means installed in all connection paths connecting the demultiplexing WSS and the combined WSS between different directions. It's fine. In the following description, the configuration of the wavelength conversion means used in the optical communication node of the present invention will be described on the premise of the configuration of FIG.

[Structure of wavelength conversion means]
As the wavelength conversion means 24a to 24d in the optical communication node of FIG. 4, an all-optical wavelength conversion means can be used. Here, the all-optical wavelength conversion means is one that performs wavelength conversion only on the optical layer without performing optical-electrical-optical conversion (O / E / O conversion). As will be described later, the wavelength conversion means 24a to 24d in the optical communication node of the present invention perform wavelength conversion by utilizing the nonlinear optical phenomenon of the optical layer. Since the all-optical wavelength conversion means does not involve an electric layer, it has merits in all aspects such as deployment cost, power consumption, component failure rate, and complicated operation.

Referring to FIG. 4 again, for example, the signal light 78 is input to one wavelength conversion means 24a, and the pump light 77 for causing wavelength conversion is input. The pump light 77 is generated by the pump light generation means 25-1 as one of the plurality of pump lights, and is input to the wavelength conversion means 24a to 24d via the WSS26-1 having an M × p configuration. The pump light is also called an excitation light, and the pump light generating means corresponds to the excitation light generating means. Hereinafter, a WSS having a configuration in which the number of input ports is M and the number of output ports is p is referred to as M × p WSS. The number of output ports p in M × p WSS26-1 is p = (N-1) × q. Here, N is the number of routes in the optical communication node, and q is the maximum number of routes including the wavelength conversion means in the connection path from one route to the other.

In FIG. 4, the value of q is the same for all connection paths, and N = 3 and q = 2, so that the number of output ports p in M × p WSS26-1 in the pump light generating means is 2 × 2 =. It becomes 4. If the number of q is the same in all connection paths as in the optical communication node of FIG. 4, all ports of M × p WSS can be used without excess or deficiency. The number of input ports M in the M × p WSS26-1 will be described later. In the optical communication node of the present invention of FIG. 4, the pump light is supplied from one pump light generating means to the connection path from one demultiplexing WSS. FIG. 14 illustrates an optical communication node that supplies pump light in a different configuration.

As the all-optical wavelength conversion means, wavelength conversion using four-wave mixing in an optical fiber or a nonlinear crystal can be used. In addition, mutual gain modulation of semiconductor optical amplifiers may be used. As the means for performing wavelength conversion, there is a drawback that power consumption increases because an electric layer is interposed, but OE conversion and EO conversion may be accompanied without using the all-optical wavelength conversion means. In this case, the pump light generating means 25-1 to 25-3 and the M × p WSS are not required. Next, a more specific configuration of the pump light generating means used together with the wavelength converting means will be described.

[Structure of pump light generating means]
FIG. 5 is a diagram showing a more specific configuration of the pump light generating means in the optical communication node of the present invention. The pump light generating means (excitation light generating means) shown in FIG. 5 includes an excitation light generation unit 25a and an excitation light frequency shift unit 25b. The pump light generating means shown in FIG. 5 includes M × p WSS26-1 to 26-3 in FIG. 4 as an excitation light selective distribution unit 26. In the excitation light generation unit 25a of FIG. 5, first, the continuous light (CW light) output by the laser diode light source LD41 is input to the photodetector PD43 via the gas cell 42. The optical signal received by the PD 43 is converted into an electric signal and input to the control circuit 44. The control circuit 44 has a mechanism for controlling the injection current into the LD 41. Therefore, the LD 41, the gas cell 42, the PD 43 and the control circuit 44 form a feedback loop that controls the output wavelength from the LD 41. By applying a weak modulation to the injection current to the LD41 in this loop, a control loop that locks the oscillation wavelength of the LD41 is configured on the absorption line of the gas cell 42. As a result, at point 60, the oscillation wavelength of the output light from the LD 41 is locked very precisely to the desired wavelength.

A part of the CW light output from the LD 41 is intensity-modulated at the frequency f by the intensity modulator 45, and a pulse is generated at the point 61. The generated pulsed light is amplified by the Erbium Doped Optical Fiber Amplifier (EDFA) 46 and then input to the highly nonlinear fiber HNLF47. At point 62, the HNLF 47 produces supercontinuum light (frequency comb) by self-phase modulation. Here, the frequency interval of the frequency comb is the frequency f.

As for the frequency comb generated by the HNLF 47, one CW light having a desired pump frequency is selected from the frequency comb lights by 1 × M WSS48. At point 63, the selected CW light is input to the SSB (Single Side Band) modulator 49. Therefore, the 1 × M WSS48 functions as a comb separation means for spatially demultiplexing the frequency comb light into a single CW light for each comb frequency. At the output of 1 × M WSS48, a maximum of M SSB modulators are provided in parallel. In the SSB modulator 49 driven by the modulation frequency Δf, the frequency of the input CW light is finely adjusted. The finely tuned CW light is amplified by the EDFA 50 and then output from the frequency shift unit 25b. The modulation frequencies Δf in the maximum M SSB modulators provided in parallel may be different from each other.

The maximum M finely tuned CW lights from the frequency shift unit 25b are first combined by the M × 1 WSS 52 in the excitation light selective distribution unit 26. Further, it is demultiplexed by 1 × p WSS53 and output to predetermined output ports 54a to 54d as excitation light which is CW light having a desired wavelength. The CW light of a desired wavelength output to any of the output ports 54a to 54d is supplied to the wavelength selection means as the pump light from the pump light generation means in FIG. The output ports 54a to 54d are connection terminals connected to the wavelength conversion means 24a to 24d in FIG. 4, and the above-mentioned CW light is input to the wavelength conversion means 24a to 24d, respectively. The CW light output from the EDFA 50 of the frequency shift unit 25b is partially branched without passing through the excitation light selective distribution unit 26, and the branch light 51 is pumped by the pump light generation means 25-1 to 25-3. It may be used as pump light.

Therefore, the pump light generation means, that is, the excitation light generation means, has a single excitation light generation unit 25a that generates frequency comb light from CW light and the frequency comb light generated by the excitation light generation unit for each comb frequency. Com Separation means 48 that spatially demultiplexes to CW light, a plurality of frequency shift units (SSB modulators) 49 that shift the frequency of the single demultiplexed CW light, and the plurality of frequency shift units. It can be carried out as including the excitation light selective distribution means 52 and 53 that combine the CW light whose frequency is shifted from each and spatially demultiplex the CW light.

FIG. 6 is a diagram showing a spectrum of the pump light generation process in the pump light generation means. Each point in the following description corresponds to points 60 to 66d of the pump light generating means of FIG. At point 60, which is the output of the wavelength control loop, the oscillation wavelength of the LD41 is locked to one of the absorption spectra of the gas cell and is output as CW light. At the point 61, which is the output of the intensity modulator 45, the CW light is intensity-modulated to generate a sideband wave. After the intensity-modulated light wave is amplified by EDFA46, it produces supercontinuum light by self-phase modulation in the highly nonlinear fiber. As a result, at point 62, which is the output of the HNLF 47, the spectrum becomes a frequency comb light 67 over a very wide band. Here, the interval of the frequency comb light is the intensity modulation frequency f.

At the point 63 which is the output of 1 × M WSS48 of the frequency shift unit 25b, a desired spectrum of the frequency comb light 67 is output to each output port of 1 × M WSS48 one wave at a time. At point 63, the CW light 68 is output as it is. The frequency of this CW light is shifted by Δf at the point 64, which is the output of the SSB modulator 49, and is finely adjusted. Further, at point 65, which is the combined wave output of the M × 1 WSS 52, a plurality of CW lights from different SSB modulators are combined. FIG. 6 shows a state in which three waves are combined. Finally, at each of the points 66a to 66d of the output port of the 1 × p WSS53, the pump light, which is the CW light of the desired wavelength, is distributed one by one. CW light from different SSB modulators is distributed and output one wave at a time to each output port of 1 × p WSS53, but as shown in FIG. 6, pump lights of the same wavelength 69-1, 69-2. May be distributed to multiple output ports. FIG. 6 shows an example of outputting CW light 69-1 and 69-2 having the same wavelength to two output ports 54b and 54d of 1 × p WSS53. The method of distribution output will be described in detail in Examples described later.

In the pump light generating means shown in FIG. 5, the pump light having a required wavelength can be extracted as CW light by the wavelength filter function of the M × 1 WSS 52 in the excitation light selective distribution unit 26. Therefore, the SSB modulator 49 of the frequency shift unit 25b in FIG. 5 may be replaced with a phase modulator or an intensity modulator that generates a double-sided band wave. That is, unnecessary sideband waves and carrier waves generated in the alternative modulator of the SSB modulator 49 can also be removed by the filter function of M × 1 WSS. Next, a specific configuration of the wavelength conversion means 24a to 24d in the optical communication node of FIG. 4 will be described.

[Structure of wavelength conversion means]
FIG. 7 is a diagram showing a configuration example of a wavelength conversion means in the optical communication node of the present invention. The wavelength conversion means 24 includes an optical merging device 70 that merges the pump light 77 and the signal light 78, and a nonlinear optical medium 72 that converts the wavelength of the signal light. When the intensities of the pump light and the signal light merged by the optical merging device 70 are insufficient to generate the nonlinear phenomenon, they can be optically amplified by the EDFA 71 and then input to the nonlinear optical medium 72.

As the optical combiner 70, an optical directional coupler or a wavelength selection switch can be used. Further, as the nonlinear optical medium 72, a highly nonlinear optical fiber, a periodic polarization inversion LiNbO ₃ waveguide, a semiconductor optical amplifier, or the like can be used. Further, the optical amplifier described as EDFA in each element of the optical communication node of the present invention may use a semiconductor optical amplifier instead.

FIG. 8 is a diagram illustrating a spectrum of each part in the wavelength conversion means of the optical communication node of the present invention. Each point in the following description corresponds to points 73 to 76 of the wavelength conversion means 24 in FIG. 7. At points 73 and 74, which are the two inputs of the wavelength conversion means, pump light 81 and signal light 82 having different wavelengths are input, respectively. At point 75, which is the output of the optical combiner 70, the above two waves are combined. Then, at the point 76, the idler light 84 is generated by the degenerate four-wave mixing by the nonlinear optical medium 72. Assuming that the optical frequency of the pump light 81 is fp and the optical frequency of the signal light 82 is fs, the optical frequency fi of the idler light 84 is expressed by the following equation.
fi = 2fp-fs equation (1)
Further, in the nonlinear optical medium 72, the idler light 83 generated by using the signal light as the pump light and the pump light as the probe light is also generated at the same time as the generation of fi.

The wavelength conversion means 24c and 24d in the optical communication node of FIG. 4 are connected to WSS29-2 (Egress2) for combined waves in the optical communication node of FIG. The original pump light 81, signal light 82 and unnecessary idler light 83 shown in FIG. 8 are removed by the filtering function of WSS29-2 for combined waves, and only the optical signal 84 (idler light) after wavelength conversion is removed. It is output to point 80-2, which is the output port of WSS29-2 for combined waves. In FIG. 8, the spectrum of the idler light 84 only is shown for the purpose of explaining the wavelength conversion operation, but at point 80-2 in FIG. 4, an optical signal transmitted without wavelength conversion or light converted to another wavelength is shown. The signal is combined and output.

[Structure for wavelength conversion of optical signals of multiple wavelengths]
In the description of the spectrum in FIG. 8 above, an example is shown in which the pump light is used only for wavelength conversion of an optical signal of a specific wavelength of an optical communication node. However, by using the pump light generating means shown in FIG. 5, it can also be used to simultaneously perform wavelength conversion of optical signals having a plurality of wavelengths in the optical communication node 20 of the present invention. In the pump light generating means of FIG. 5, one CW light is selected from the frequency comb light 67 by 1 × M WSS48, a plurality of SSB modulators are operated in parallel and independently, and pump light of different wavelengths is output at the same time. Because it can be done. This is effective when the wavelengths of two different optical signals are exchanged with each other. That is, it can be applied when an optical signal having an optical frequency of fs2 is converted to fs4 and an optical signal having an optical frequency of fs4 is converted to fs2.

FIG. 9 is a diagram illustrating and explaining the operation when the wavelength conversion of the two optical signals is performed collectively and the operation when the wavelength conversion is divided by the pump light generating means shown in FIG. 5. FIG. 9A describes an operation in which an optical signal having a frequency fs2 and an optical signal having a frequency fs4 are collectively introduced into the nonlinear optical medium 72 of the wavelength conversion means of FIG. 7 to perform wavelength conversion. At point 75, which is the output of the optical confluence 70, there are three wavelengths including pump light of frequency fp. The optical spectrum at the point 76, which is the output of the nonlinear optical medium 72, is a mixture of the residual component of the signal light of fs2 and the converted fi4. Similarly, the residual component of the signal light of fs4 and the converted fi2 are mixed. Since these mixed signals have the same wavelength, they cannot be separated by the filtering function of the WSS29-2 at the point 80-2, which is the output port of the optical communication node 20, for example, the WSS29-2 for combined waves.

FIG. 9B is a diagram illustrating an operation of performing wavelength conversion with CW light 69-1 and 69-2 having the same wavelength in the pump light generating means shown in FIG. As shown in FIG. 9B, the conversion of fs2 → fi2 (= fs4) and the conversion of fs4 → fi4 (= fs2) are performed using CW light 69-1 and 69-2 of the same wavelength, and have different wavelengths. It is done by conversion means. In this case, it is possible to avoid mixing the residual component of one signal light and the converted light component of the other signal light described in FIG. 9A. That is, the pump lights 69-1 and 69-2 having an optical frequency of fp are distributed to the output ports 54b and 54d of the 1 × p WSS53, respectively, and are individually performed by the wavelength conversion means 24d and 24b.

The upper figure of FIG. 9B shows a case where the signal light fs2 is converted into fs4 by the wavelength conversion means 24d. The unnecessary signal 85 of the residual component of the pump light fp and the original signal light fs2 is filtered by the combined wave WSS29-2, and only the signal light fs4 after wavelength conversion is extracted at the point 80-2. The lower figure of FIG. 9B shows a case where the signal light fs4 is converted to fs2 by the wavelength conversion means 24b. As in the case of the wavelength conversion means 24d, the unnecessary signal 86 is filtered by the combined wave WSS29-3, and only the signal light fs4 after the wavelength conversion is extracted at the point 80-3. As described above, in the optical communication node 20 of the present invention, the wavelengths of the two signal lights can be easily exchanged. Here, an example of wavelength exchange for two waves is shown, but it is also possible to use three pump lights of the same wavelength for mutual wavelength conversion of three or more signal lights. Outputting CW light of the same wavelength at points 66b and 66d of the two output ports of the 1 × p WSS53 described here is realized by using the broadcast function of the wavelength selection switch described later in the second embodiment.

The optical communication node of the present invention shown in FIG. 4 can realize more flexible and simple wavelength defragmentation as compared with the prior art. By performing wavelength conversion on the path within the optical communication node without changing the frequency of the transmitter at the transmission node, the troublesome and complicated control required across multiple communication nodes is greatly simplified. The node. If the information about the wavelength change is known in the receiving node, the frequency of the local oscillator can be changed to the changed frequency (wavelength) in advance on the receiver side of the receiving node. Even in the pump light generating means, it is sufficient to prepare the pump light having a predetermined frequency in advance before the wavelength change is carried out. By changing the transmission wavelength settings of the input side WSS and the output side WSS, the wavelength of the optical signal can be changed immediately. On the receiving node side, reception with the wavelength before the change and reception with the wavelength after the change can be performed in parallel. Therefore, the wavelength can be changed without interrupting communication.

Next, in the optical communication node of the present invention, a more specific embodiment realized by using WSS in which each component is integrated will be described.

The M × p WSS26-1 to 26-3 in the optical communication node of the present invention shown in FIG. 4 is realized by connecting the M × 1 WSS 52 and the 1 × p WSS 53 shown in FIG. 5 in a longitudinal manner. Generally, in a multi-input multi-output WSS, when the wavelengths to the input ports are all different, a common port (combined port) of two WSSs can be connected as shown in FIG. If all the wavelengths to the input port are different, wavelength collision does not occur and the switch does not block internally. In the excitation light generation unit 25a and the frequency shift unit 25b in FIG. 5, since the inputs of the frequency shift unit 25b to the M × 1 WSS 52 are all different in principle, no internal blockage occurs. A WSS having the same function as the M × p WSS26-1 to 26-3 can also be realized by using a WSS having a normal 1 × (M + p-1) configuration having one combine port.

FIG. 10 is a diagram showing a configuration example of M × p WSS for selective distribution of excitation light in the optical communication node of the present invention. An example is shown in which a single WSS having a 1 × (M + p-1) configuration is used as a WSS having an M × p configuration shown in FIG. The WSS having a 1 × (M + p-1) configuration in FIG. 10 is composed of (M + p) input / output ports 101, a diffraction grating 102, a cylindrical lens 103, 104, and a deflection element 105. FIG. 10 shows a view of the array plane (x-z plane) of the input / output ports 101 with the z-direction, which is the traveling direction of light, as the horizontal direction of the drawing, and the side surface (y-z plane) orthogonal to the arrangement plane (x-z plane). It consists of the figure you saw. Of the (M + p) input / output ports 101, M are used as input ports 101a and p are used as output ports 101b. CW light having different wavelengths is input to each of the M input ports 101a. For example, the CW light input from the input port 101-2 propagates along the optical path of the alternate long and short dash line. The CW light is first wavelength-demultiplexed by the diffraction grating 102 and dispersed in the yz plane in the direction corresponding to the wavelength of the CW light. The CW light is further refracted in the x-z plane by the cylindrical lens 103, then refracted in the y-z plane by the cylindrical lens 104, and finally reaches the deflection element 105.

CW light input from another input port among the M input ports, for example, input port 101-3, propagates along the dotted optical path. Since this CW light has a wavelength different from that of the CW light input to the input port 101-2, it is dispersed in different directions by the diffraction grating 102. Similarly, the CW light input from the input port 101-4 is also dispersed by the diffraction grating 102 in a direction different from the above-mentioned two CW lights. Since all the CW lights input from different input ports have different wavelengths, each CW light finally lands on the deflection element 105 at different positions in the y direction. The deflection element 105 deflects each CW light so as to output to a desired port among the p output ports 101b. Each deflected CW light passes through the cylindrical lenses 104, 103 and the diffraction grating 102 and is output to any of the p output ports 101b.

As described above, the multi-input, multi-output M × p WSS constituting the M × 1 WSS 52 and 1 × p WSS 53 shown in FIG. 5 has a single 1 × (M + p-1) having one combined wave port. ) It can be realized by configuring the WSS as shown in FIG.

In the pump light generating means shown in FIG. 5, a method of outputting CW light of the same wavelength to two output ports (points 66b, 66d) of 1 × p WSS53 was described. In this embodiment, a configuration is described in which CW light of the same wavelength is output from different output ports of M × p WSS by using the broadcast function of the deflection element. LCOS (Liquid Crystal on Silicon) is used as the deflection element of WSS in this embodiment. The LCOS is a spatial phase modulation element in which pixel-shaped phase modulation elements, each of which can be individually controlled, are arranged two-dimensionally.

FIG. 11 is a diagram illustrating the configuration of the LCOS used in the M × p WSS for the selective distribution of the excitation light of this embodiment. In the LCOS 105 shown in FIG. 10, the relationship between the phase pattern displayed by the two-dimensionally arranged phase modulation elements (pixels) and the beam of CW light incident on the LCOS 105 is shown. On the left side of FIG. 11, pixels arranged two-dimensionally on the LCOS are seen, three CW lights are incident, and the beam planes 106a, 106b, 106c of the respective CW lights are drawn. At this time, each CW light lands at its center position 105a in the x direction and at a different position in the y direction.

Different phase modulation patterns can be displayed depending on the pixels in the area occupied by each CW light on the LCOS. For example, the phase pattern 107-2 is displayed in the region 106-2 covered by the beam surface 106a of the CW light shown by the alternate long and short dash line. Similarly, the phase pattern 107-3 is displayed in the region 106-3 covered by the beam surface 106b shown by the dotted line, and the phase pattern 107-4 is displayed in the region 106-4 covered by the beam surface 106c shown by the solid line. do.

Each phase pattern is a saw-like pattern in which the phase value is folded back at 2π, and the polarization direction of the incident light is adjusted by the pattern period. For example, the phase pattern 107-2 has a constant pattern period Λ1, and all CW light on the beam surface 106a is deflected in the same direction. The phase pattern 107-3 is composed of a phase pattern having pattern periods Λ2 and Λ3 with the center line 105a as a boundary. At this time, the component of the CW light 106b incident on the region of the pattern period Λ2 and the component of the CW light 106b incident on the region of the pattern period Λ3 are deflected in different directions. The phase pattern 107-4 has three components having a pattern period of Λ4, Λ5, and Λ6, and the components of the CW light 106c incident on each region are deflected in different directions.

As described above, one CW light is produced by incident CW light so that the beam plane of the CW light incident on the LCOS 105 is divided into regions on the LCOS and deflected by different phase patterns in each region. Can lead to different output ports of M × p WSS. That is, CW light having the same wavelength can be output to two different output ports of 1 × p WSS53 in FIG. 5 and introduced into the two wavelength conversion means.

In this embodiment, a specific configuration example of each wavelength combiner / demultiplexer in the pump light generator in FIG. 5 will be described. In the pump light generation unit shown in FIG. 5, three units of 1 × M WSS48, M × 1 WSS52, and 1 × p WSS53 are required as WSS having a wavelength combined / demultiplexing function. In the second embodiment, the configuration in which M × 1 WSS 52 and 1 × p WSS 53 for selective distribution of excitation light are realized by a single optical system has been described. In this embodiment, a configuration in which three WSS units are integrated in a single optical system will be described by further adding 1 × M WSS48.

Before explaining the details of WSS integration, a spatial beam transformer (SBT) will be described. The SBT is a circuit element formed in the optical waveguide element, and is an important component for promoting the integration of WSS.

FIG. 12 is a diagram showing an outline of the configuration of the spatial beam converter. The SBT 200 includes a plurality of input waveguides 201, a slab waveguide 202, and an array waveguide 203 formed on the substrate. The optical signal input to the input waveguide 201 reaches the array waveguide 203 while spreading in a plane parallel to the substrate surface in the slab waveguide 202. The array waveguide 203 is configured so that the optical path lengths of the adjacent waveguides are equal to each other. The optical signal that reaches the array waveguide 203 is output to free space from the chip end 204 while maintaining its wavefront. Here, the direction of the wavefront of the optical signal output from the chip end 204 in the free space is determined depending on which of the input waveguides 201 the optical signal is input from. For example, the optical signal input from the input waveguide 201a is output in the direction of the light ray 205a, and the optical signal input from the input waveguide 202b is output in the direction of the light ray 205b.

FIG. 13 is an optical path diagram of an optical system in which three WSSs are integrated in the pump light generating means used in the optical communication node of the present invention. In the optical system shown in FIG. 13, the three WSSs of 1 × M WSS48, M × 1 WSS52, and 1 × p WSS53 in FIG. 5 are integrated. In the following description, the optical path diagram of FIG. 13 is orthogonal to a view of an array plane (x-z plane) of M + p input / output ports with the traveling direction z of light as the horizontal direction of the drawing. It consists of a view of a side surface (yz plane). In the integrated WSS of this embodiment, an optical waveguide chip 301 containing at least M + p SBT circuit elements is used as an input / output port.

First, the operation as 1 × M WSS48, which is a comb separation means for separating a plurality of CW lights, will be described. The CW light 300b input from the input port 301b is output to the free space in the optical path direction of the dotted line 303b via the SBT circuit element 302b. This CW light is wavelength-demultiplexed by the diffraction grating 102 and then reaches the deflection element 105 via the cylindrical lenses 103 and 104. As in the second embodiment, it is preferable to use the LCOS element as the deflection element 105. As described above, the CW light 300b is tilted in the direction of the light beam 303b in the x-axis direction and is output to the free space. Therefore, even on the LCOS element, it lands at the position 105b offset in the x direction from the intersection 105a with the optical axis.

The deflection element 105 deflects the CW light in the direction of any one (SBT circuit element 305b) constituting the desired output port for each wavelength of the CW light in the SBT circuit element group 305, and the dotted line 304b. Follow the optical path of. In the integrated WSS shown in FIG. 13, basically one SBT circuit element outputs one wavelength of CW light. Signals having the same frequency adjustment amount Δf by the SSB modulator 49 for frequency shift in FIG. 5 may be collectively output to the same output port. In the example of the optical path diagram of FIG. 13, among the CW light deflected by the deflection element (LCOS) 105, the optical signal having the wavelength indicated by the dotted line propagates in the direction of the light ray 304b and is output via the SBT circuit element 305b. It is output from port 306b.

The operation as the M × p WSS (M × 1 WSS 52 and 1 × p WSS 53) as the excitation light selective distribution unit is as follows. Of the input waveguides connected to the SBT circuit element group 305, CW light is input to, for example, the SBT circuit element 305b in a waveguide that is not used as an output port of the 1 × M WSS48. This CW light is CW light from one of the plurality of SSB modulators of the frequency shift unit 25b in FIG. The input CW light 300c is output from the end of the SBT circuit element 305b to the free space in the direction of the solid line 303c. The CW light 300c lands on the point 105c on the LCOS 105 via the diffraction grating 102 and the cylindrical lenses 103 and 104. Here, the landing position 105c is different from the intersection 105a of the optical axis and the LCOS 105 for the same reason as in the case of the above-mentioned CW light 300b. Since the light rays 303b and the light rays 303c, which are the emission directions to the space, are in different directions, the points 105b and 105c at the two landing positions are also different points. Therefore, the LCOS 105 can integrate 1 × M WSS48 and M × p WSS into one optical system by displaying different phase patterns in the vicinity of the points 105b and 105c in the x direction. The CW light 300c is finally output to an output waveguide connected to any one of the SBT circuit element groups 307. In FIG. 13, the output is from the output port 307c.

As described above, according to the configuration of this embodiment, the three WSSs (1 × M WSS48, M × 1 WSS52 and 1 × p WSS53) required for the pump light generation means shown in FIG. 5 are combined into a single optical system. Can be accumulated in. That is, the wavelength selection switch 1 × M WSS48, which is a comb separation means, can share the same optical system as the multi-input multi-output wavelength selection switch (M × 1 WSS 52 and 1 × p WSS 53). It is possible to efficiently integrate the components of the pump optical generation means added in the optical communication node of the present invention and realize the miniaturization of the node device in the optical communication node.

In the optical communication node of the present invention shown in FIG. 4, a configuration having a wavelength conversion means and a corresponding pump light generation means for each input route has been described. That is, the pump light generating means 25-1 and the M × p WSS26-1 were provided for the path 22-1 from the demultiplexing WSS22-1 of the input route In1. Similarly, the pump light generating means 25-2 and the M × p WSS26-2 were provided for the path 22-2 from the demultiplexing WSS22-2 of the input route In2. The same applies to the path 22-3 from the demultiplexing WSS 22-3 of the input route In3. However, if the intensity of the pump light is sufficient, the pump light can be supplied from one pump light generating means across different directions.

FIG. 14 is a diagram showing another configuration example of the optical communication node of the present invention. In the optical communication node 400 of FIG. 14, pump light is supplied from one pump light generating means 25 to all wavelength conversion means in the three directions (In1 to In3) via M × p WSS401. The output port of the M × p WSS401 is connected not only to the wavelength conversion means 24a to 24d in the direction In1 but also to all the other wavelength conversion means of the directions In2 and In3. Therefore, the number of ports p in the M × p WSS401 is equal to the total number of wavelength conversion means in this optical communication node.

In the optical communication node of this embodiment, an example in which the number of wavelength conversion means is equal to that of p is shown, but the numerical value of p is not limited to this example. By supplying pump light to the wavelength conversion means corresponding to a plurality of directions by a single pump light generating means, it is possible to realize miniaturization and cost reduction of the device in the optical communication node.

In the optical communication node of each of the above-described embodiments, the wavelength conversion means is a plurality of paths connecting each of the plurality of demultiplexing wavelength selection switches and each of the plurality of combined wave wavelength selection switches to each other. It is installed in at least one. In this configuration, it cannot be applied between two adjacent nodes where there is no relay node between them. However, there may be a case where it is desired to immediately perform wavelength conversion on the optical signal from the Add port of the optical communication node. In this embodiment, the configuration of an optical communication node suitable for the case where the wavelength fragmentation in the optical signal to be added is severe is presented.

FIG. 15 is a diagram showing still another configuration of the optical communication node of the present invention. The optical communication node 500 of FIG. 15 further adds a wavelength conversion means on the path from the Add port 28 to the optical communication node 400 shown in FIG. Other configurations are the same as in FIG. 14, so only the differences will be described. In the optical communication node of FIG. 15, two paths 503 are configured from the Add port 28 to each of the three wavelength selection switches 29-1 to 29-3 for combined waves. Wavelength conversion means 24e to 24j are installed on each path 503. Pump light is supplied from one pump light generator 25 via the M × p WSS501 to the path between the input and output paths and to all wavelength conversion means on the path 503 from the Add port 28. Will be done. In FIG. 15, pump light is supplied from the output 502 of the M × p WSS501 to the wavelength conversion means 24e to 24j.

In the optical communication node of this embodiment, the output port of M × p WSS401 is connected not only to the directions In1, In2, In3 but also to all the wavelength conversion means existing on the path connected to Out1, Out2, Out3. Will be done. Therefore, in the case of the configuration of FIG. 15, the number of ports p in M × p WSS501 is equal to the total number of wavelength conversion means in this optical communication node, and the number of output ports p is p = N × q. In the optical communication node of this embodiment, an example is shown in which the number of ports p of the excitation light selective distribution unit 26 and the number of wavelength conversion means are equal, but the numerical value of p is not limited to this example. If an empty port in the excitation light selective distribution unit 26 is allowed, pump light may be supplied to each wavelength conversion means by any number and combination method of pump light generation means.

By supplying pump light with a single pump light generating means to the wavelength conversion means corresponding to a plurality of directions including the Add port, it is possible to realize miniaturization and cost reduction of the device in the optical communication node. That is, the wavelength conversion means is installed in the path from the Add port connected to the plurality of combined wave wavelength selection switches, which is at least one of the paths connected to the plurality of combined wave wavelength selection switches. Has been done.

By providing the wavelength conversion means for the path on the Add port 28 as well, the wavelength is converted immediately after the transmitter, but the wavelength can be switched more flexibly in the entire optical communication system. Wavelength defragmentation is performed by performing wavelength conversion of the added optical signal, such as when the wavelength fragmentation of the added optical signal is more severe than the wavelength fragmentation state of the optical signal passing through In1, In2, In3, etc. In some cases, the number of wavelengths converted may be smaller. Therefore, in addition to the configuration of the embodiment shown in FIG. 14, more flexible wavelength defragmentation can be realized by enabling wavelength conversion on the path of the Add port as in the present embodiment. As a matter of course, the configuration provided with the wavelength conversion means for the Add port of this embodiment can also be applied to the configuration of the optical communication node of FIG. 4 described first.

According to the present invention, more flexible and simple wavelength defragmentation can be realized as compared with the prior art. By performing wavelength conversion on the path in the optical communication node without changing the frequency of the transmitter in the transmission node, troublesome and complicated control between a plurality of communication nodes is greatly simplified. If the information about the wavelength change is known in the receiving node, the frequency of the local oscillator may be changed to the changed frequency (wavelength) in advance on the receiver side of the receiving node. Even in the pump light generating means, it is sufficient to prepare the pump light having a predetermined frequency in advance before the wavelength change is carried out. By changing the transmission wavelength settings of the input side WSS and the output side WSS, the wavelength of the optical signal can be changed immediately. On the receiving node side, reception with the wavelength before the change and reception with the wavelength after the change can be performed in parallel. Therefore, the wavelength can be changed without interrupting communication. The components such as the pump light generating means and the pump light selective distribution means added by the present invention can realize the related device in a small size and at low cost by using the WSS integrated in the optical plane circuit.

In Examples 1 to 5 described above, the configuration of an optical communication node for performing flexible and simple wavelength defragmentation has been described. In order to carry out wavelength defragmentation while the optical communication system is actually in operation, the operation procedure of each device at each optical communication node is important. Therefore, the present invention has an aspect of an optical communication system including an optical communication node for performing wavelength defragmentation and an optical communication node at a receiving end for dropping information data. Further, in the following examples, in the optical communication system using the optical communication nodes of the first to fifth embodiments, the configuration and operation procedure of the optical communication node that does not cause a signal interruption of communication will be described. Therefore, the present invention also has an aspect as a control method of an optical communication node in an optical communication system. It also has an aspect as a receiving end optical communication node that implements a control method between optical communication nodes in an optical communication system.

As described in the spectra of the pump light generating means of FIG. 6 and the wavelength conversion means of FIG. 8, wavelength defragmentation utilizes a wavelength conversion means which is an all-optical wavelength conversion means based on a nonlinear optical effect. In the wavelength conversion by the nonlinear optical effect, unnecessary light is generated in addition to the signal light after the final conversion. Specifically, as shown in FIG. 8, a signal light 82, a pump light 81, an idler light 83 using these as probe light, and an idler light (signal light) 84 which is a desired wavelength conversion light are simultaneously generated. In the node that performs wavelength conversion, it is necessary to operate the optical communication system by using only the signal light 84, which is the idler light of the wavelength after wavelength conversion, among these lights. The pump light 81 having an unnecessary wavelength, including the signal light 82 before the wavelength conversion, and the idler light 83 generated by the nonlinear optical effect are blocked by, for example, WSS29-1 to 29-3 for combined waves in FIG.

However, when trying to switch the wavelength of an optical signal while the optical communication system is in an operating state, there is a problem that communication is interrupted at the moment of switching. Here, the wavelength of the optical signal before wavelength conversion is λ1, and the wavelength of the optical signal after wavelength conversion is λ2. In the optical communication node that performs wavelength conversion and the optical communication node at the receiving end that drops the optical signal, if the wavelength change setting from λ1 to λ2 is performed for each device such as WSS and other filters, it is necessary for resetting. Communication is interrupted during a short period of time. Hereinafter, an optical communication node that drops an optical signal transmitting information data is referred to as a receiving end node.

In order to avoid the above-mentioned communication blackout, it is also possible to simultaneously transmit two optical signals having different wavelengths of λ1 and λ2 to the receiving end node. In this case as well, the reception timing is set between two optical signals with different wavelengths on the receiving end node side due to the influence of wavelength dispersion in the transmission line and the difference in the length of the in-station wiring (optical fiber) in the receiving end node. There will be a gap. At the receiving end node, the dropped optical signal is connected to a transponder or the like corresponding to the wavelength, and after the wavelength demultiplexing on the stage side after the demultiplexing WSS, it may have a different delay for each path corresponding to the wavelength. If the wavelength switching operation is performed between the two wavelengths on the receiving end node side with a difference in reception timing for each demultiplexed path, signal disconnection and data loss are inevitable. Therefore, in order to avoid data loss as much as possible at the receiving end node and succeed in receiving information data, a mechanism for phase-locking two optical signals having different wavelengths and a procedure for stably performing phase-locking are important.

FIG. 16 is a diagram showing a configuration of an optical communication system according to a sixth embodiment of the present invention. FIG. 16 shows a partial configuration of an optical communication network including two optical communication nodes of node B600 and node C700. The wavelength of the optical signal is switched between the two optical communication nodes 600 and 700 without causing data loss. The two optical communication nodes 600 and 700 shown in FIG. 16 assume an example in which information is transmitted from node A to node C via node B in the arrangement status of the nodes of the optical communication network shown in FIG. ing. At node B600, wavelength defragmentation is performed to change the wavelength of the optical signal as described in Examples 1-5. The optical signal after wavelength conversion is transmitted to the node C, and this optical signal is dropped at the node C. Therefore, the node C700 becomes the receiving end node. The route settings for each node are as follows.

The optical signal of wavelength λ1 input to the input port In2 of the demultiplexing WSS603-2 in the node B600 is wavelength-converted to wavelength λ2 by the wavelength conversion means 605 on the path 612. The optical signal of λ2 after wavelength conversion is output from the output port Out1 of the combined wave WSS604-1 of the node B to the transmission line 650 and propagates to the receiving end node C. It should be noted that from Out1 of WSS604-1 for combined wave, in addition to the optical signal of λ2 after wavelength conversion, the optical signal of λ1 before wavelength conversion is output at the same time until the phase synchronization procedure described later is completed. That is what you are doing. Therefore, the combined wave WSS604-1 of the node B600 has different wavelengths (λ1, λ2) before and after the wavelength conversion from the path 612 into which the wavelength conversion means 605 is inserted to its output port Out1 until the phase synchronization procedure is completed. Note that it is set to output two optical signals.

As also described with reference to FIG. 8, in the optical communication nodes of Examples 1 to 5, the original pump light 81, the signal light 82, and the unnecessary idler light 83 are removed, and the optical signal 84 after wavelength conversion ( It has been described that only idler light) is output to the output port of WSS29-2 for combined wave (FIG. 4). In this embodiment, the original optical signal having the wavelength λ1 before wavelength conversion, which was unnecessary until the phase synchronization procedure described later is completed, is used.

The multiplexed optical signal including at least λ1 and λ2 from the output port Out1 of the combined wave WSS604-1 is input to the input port In1 of the demultiplexing WSS703-1 of the node C700 via the transmission line 650. Ru. Multiplexed light containing two optical signals of wavelengths λ1 and λ2 input to In1 is illustrated to each optical communication node of FIG. 16 via a path 710 from one of the output ports of the WSS703-1 for demultiplexing. Received by a transponder that has not. Although the node B600 and the node C700 are described as having the configuration of the optical communication node of the fourth embodiment shown in FIG. 14, each may be an optical communication node having the configuration of another embodiment. Further, the setting of the number of directions and the wavelength of each optical communication node is not limited to that of this embodiment.

The optical communication node of this embodiment includes a wavelength switching processing unit 800 on the path to the transponder on the Drop port side. The wavelength switching processing unit 800 realizes wavelength switching without data loss in conjunction with the operation of wavelength defragmentation of the optical communication node shown in Examples 1 to 5. The wavelength switching processing unit 800 includes a wavelength demultiplexing unit (DEMUX) 801 that demultiplexes two optical signals having different wavelengths λ1 and λ2, and at least two data reception paths that perform phase adjustment for the optical signals of each wavelength. It is composed of a phase synchronization control unit 803 and a signal switching unit 806 that switches between two data reception paths to perform wavelength switching.

The data reception paths are the phase adjustment units 802-1 and 802-2 for adjusting the phase of the optical signal demultiplexed from the DEMUX801, and the phase estimation units 804-1 and 804-2 for estimating the phase of each optical signal, respectively. It includes receiving units 805-1 and 805-2 that decode each optical signal. Next, a more detailed operation of the wavelength switching processing unit 800 linked with the operation of wavelength defragmentation of the optical communication node (node B) that switches the wavelength on the upstream side of the receiving end node will be described.

FIG. 17 is a diagram showing a flow of a wavelength defragmentation operation and a phase synchronization procedure in the optical communication node of the sixth embodiment. In the flow 1000, the operation of the node B600 for switching the wavelength and the operation of the wavelength switching processing unit 800 of the receiving end node C700 will be described together. As will be described later, the wavelength switching processing unit 800 operates to estimate the phases of the two optical signals and adjust the phase difference between the two. Here, the term "phase" means "timing of information data" in an optical signal transmitted by an optical communication system. Therefore, terms such as "phase estimation", "phase synchronization", and "phase adjustment" will be replaced with "information data timing estimation", "information data timing synchronization", and "information data timing adjustment", respectively. Please note. When performing wavelength defragmentation to switch the wavelength of an optical signal, the information data must not be interrupted or lost. The wavelength switching processing unit 800 on the path for dropping the optical signal at the receiving end node operates so as to match the timing of the information data of the two optical signals. The two optical signals before and after the wavelength conversion differ only in the wavelength (frequency) of the light as a carrier carrying the information data, and the contents of the carrying information data are the same. Therefore, in order to switch between two optical signals of different wavelengths at the receiving end node, it is necessary to match the timing not only by synchronizing the bits and modulation symbols but also by considering the contents of the information data. If the wavelength is switched after the timings of the information data of the two optical signals are completely matched, no data loss will occur downstream of the wavelength switching processing unit 800, or the disappearance will not hinder the use of the information data. It can be suppressed. The wavelength switching processing unit 800 at the receiving end node C can be operated in conjunction with the wavelength defragmentation at the node B for wavelength switching, and the optical communication system including the optical communication nodes of Examples 1 to 5 can be operated more stably. ..

In step 1001, for the optical signal of λ1 that performs wavelength defragmentation at the node B, the optical signal of λ2 is generated by the wavelength conversion means 605 on the path 612. As described above, it should be noted that at this stage, both the optical signals of λ1 and λ2 are wavelength-multiplexed and simultaneously output from the output port Out1 of the WSS604-1 for combined waves of the node B.

In step 1002, each optical signal of λ1 before wavelength conversion and λ2 after wavelength conversion is demultiplexed by WSS703-1 for demultiplexing of the receiving end node C700, dropped in the path 710, and input to DEMUX801. As the DEMUX801, for example, an arrayed-Waveguide Grating (AWG) or a WSS is often used.

In step 1003, the phases of the optical signals of the optical signal of λ1 and the optical signal of λ2 output from different ports of DEMUX801 are estimated by the phase estimation units 804-1 and 804-2, respectively. As described above, since the phase of the optical signal means the timing of the information data in the optical signal, the timing of the information data of the two optical signals is estimated here. In the configuration of the wavelength switching processing unit of FIG. 16, the receiving units 805-1 and 805-2 are provided on the downstream side of the phase estimation units 804-1 and 804-2, but the optical signal is branched in the phase estimation unit. Then, at least a part of the information data may be decoded to obtain the timing of the information data. Various methods can be selected as a method for obtaining the timing of the information data of the two optical signals. It can be processed as an optical signal as it is, or it can be processed once converted into an electric signal. Further, the processing at the intermediate frequency before decoding, the processing at the signal after decoding, or a combination thereof can also be used. As will be described later, since the wavelength switching processing unit obtains the phase difference (timing difference), the timing of the information data does not have to be an absolute time, but may be a relative timing from a specific time.

In step 1004, the phase difference between the optical signal of λ1 and the optical signal of λ2 is calculated from the above two phase estimates. It is determined whether or not this phase difference exceeds the variable range of the phase that can be adjusted by the phase adjusting unit 802-2 with respect to the optical signal of λ2. As described above, the phase adjustment unit can be paraphrased as a timing adjustment unit, and the timing difference may be obtained instead of the phase difference, and the variable range of the timing adjustment in the timing adjustment unit 802-2 may be determined.

In the steps from step 1001, the signal switching unit 806 in the final stage of the wavelength switching processing unit 800 selects the optical signal of λ1 before the wavelength conversion. It should be noted that the decoded output of the optical signal of λ1 from the 805-1 receiver is further supplied to a transponder or the like in the subsequent stage, and information data is transmitted. By the procedure after step 1003 described below, wavelength switching without data loss is prepared from the optical signal of λ1 to the optical signal of λ2. If the phase difference in step 1004 does not exceed the variable range of phase adjustment in the phase adjustment unit 802-2 (NO), the flow 1000 proceeds to step 1005.

In step 1005, the phase synchronization control unit 803 gives the phase adjustment unit 802-2 to the optical signal of λ2 so that the two optical signals of λ1 and λ2 are phase-locked, that is, the timings of the information data match. Find the power phase shift amount. The obtained phase shift amount is applied to the phase adjustment unit 802-2, and a feedback operation is performed to shift the phase of the optical signal of λ2 so as to eliminate the phase difference calculated in step 1004. The phase synchronization control unit 803 can operate as a timing synchronization control unit, and the phase shift can be paraphrased as a timing shift (timing adjustment) of data information. If the phase difference between the two optical signals in step 1004 exceeds the variable range of phase adjustment by the phase adjustment unit 802-2 (YES), the procedure proceeds to step 1008.

In step 1008, under the control of the phase synchronization control unit 803, the phase difference (corresponding to the remaining amount) exceeding the variable range of the phase adjustment for the optical signal of λ2 is used as the phase shift amount for the phase adjustment for the optical signal of λ1. It is given to the unit 802-1 and the optical signal of λ1 is phase-shifted. After that, the procedure returns to step 1003, and the phases of each of the two optical signals of λ1 and λ2 are estimated again by the phase estimation units 804-1 and 804-2. In the stage after returning from step 1008, the initial phase difference between the optical signal of λ1 and the optical signal of λ2 is reduced by the phase adjustment by the phase adjusting unit 802-1 for the optical signal of λ1 carried out in step 1008. ing. Therefore, the determination in step 1004 after passing through step 1008 is NO, and the process proceeds to step 1005 described above.

In step 1006, it is determined whether or not the phase difference between the optical signal of λ1 and the optical signal of λ2 is equal to or less than the allowable value. Needless to say, the phase difference is replaced by the timing difference between the optical signal of λ1 and the optical signal of λ2. Here, if the phase difference (timing difference) exceeds the allowable value (NO), the process proceeds to step 1009.

In step 1009, the phase shift amount to be given to the phase adjustment unit 802-2 for the optical signal of λ2 in order to eliminate the phase difference between the two optical signals is calculated by the control of the phase synchronization control unit 803. Returning to step 1005 again, under the control of the phase synchronization control unit 803, the optical signal of λ2 is phase-shifted by the phase adjustment unit 802-2, and a feedback operation is performed. The number of repetitions of step 1009 varies depending on parameters such as the phase control amount and loop gain of the feedback loop control of one operation, and depends on the specific control method and algorithm of the phase synchronization control unit 803. The allowable value of the above-mentioned phase difference is determined according to the rate of information transmission in the optical communication system and the modulation method of the optical signal. If the transmission rate (that is, baud rate) of information data is high, or if the modulation method has a large modulation order, the allowable value of the phase difference (timing difference) can be set strictly. If the phase difference between the optical signal of λ1 and the optical signal of λ2 is equal to or less than the allowable value in step 1006 (YES), the procedure proceeds to step 1007.

In step 1007, the signal switching unit 806 in the final stage of the wavelength switching processing unit 800 switches the path so as to output the optical signal of λ2, and the procedure of the flow 1000 is completed.

In the procedure in steps 1004, 1005 and step 1008 described above, in order to eliminate the phase difference between the optical signal of λ1 and the optical signal of λ2, the phase adjusting unit 802-2 for the optical signal of λ2 after wavelength conversion was used. Priority is given to phase adjustment. Since the optical signal of wavelength λ1 before wavelength conversion is the original data information and is the optical signal that information is actually transmitted before the wavelength switching, do not carelessly manipulate the optical signal of λ1 as much as possible. This is because it is preferable. Therefore, it is desirable to preferentially adjust the phase adjusting unit 802-2 of the optical signal of λ2 without operating the phase adjusting unit 802-1 of the optical signal of λ1 as much as possible. As in step 1008, only when the phase difference between the optical signal of λ1 and the optical signal of λ2 exceeds the operating range of the phase modulation unit 802-2 on the λ2 side, the phase adjustment unit phase modulation unit 802 of the optical signal of λ1 It is desirable to operate -1.

Therefore, the present invention presents a plurality of wavelength division wavelength selection switches (603-) for demultiplexing wavelength-divided multiplex signals from different input routes in an optical communication system that multiplexes optical signals of different wavelengths and transmits information data. 1-603-3), a plurality of wavelength-dividing wavelength selection switches (6041-1604) for merging wavelength-divided multiplex signals including the demultiplexed signal light from each of the plurality of demultiplexing wavelength selection switches. -3), and the plurality of paths that are interconnected between each of the plurality of demultiplexing wavelength selection switches and each of the plurality of combined wave wavelength selection switches are provided, and the plurality of combined waves are provided. Wavelength conversion is performed in the first optical communication node 600 in which the wavelength conversion means 605 is installed and the first optical communication node for at least one path 612 of the paths connected to the wavelength selection switch. The wavelength demultiplexing means 703-1 and 901 for wavelength-dividing the previous first optical signal and the second optical signal obtained by converting the wavelength of the first optical signal into wavelengths, and the first optical signal and the first optical signal. Timing estimation units 904-1, 904-2 for estimating the timing of information data between the second optical signals, and the timing difference of the information data between the first optical signal and the second optical signal. It is provided with a wavelength switching processing means 900 including a timing adjusting unit 903, 904-1, 904-2, and a second optical communication node 700 for dropping the second optical signal carrying the information data. It can be implemented as an optical communication system.

Further, in the above-mentioned optical communication system, a step of performing wavelength conversion on the first optical signal of wavelength λ1 and generating the second optical signal of wavelength λ2 at the first optical communication node. At the second optical communication node, a step of estimating the timing of the first optical signal and the second optical signal by the timing estimation unit, and at the second optical communication node, the first optical signal. And the step of operating the timing adjusting unit so that the timing difference of the second optical signal is reduced, and the second optical communication node receives the first optical signal to the second optical signal. It includes a step of switching directions and acquiring the information data from the second optical signal, and a step of deleting an optical path related to λ1 in the first optical communication node and the second optical communication node. It can also be implemented as a control method for an optical communication node that implements a phase synchronization procedure.

The phase adjustment accuracy in the phase adjustment units 802-1 and 802-2 is 0.01 to 0. When converted into time based on the standards in the 100G system and the system called Beyond 100G, which are currently being introduced as an example. It will be about 1 nsec. Since the information transmission speed in the current optical communication is ^{about 25 to 50 × 10 9} baud, a phase (timing) adjustment accuracy corresponding to the reciprocal of this transmission speed is required. Further, as for the variable range of the phase adjustment, if there is a variation in the length of the optical fiber in the station in terms of vacuum, an adjustment range of about 30 nsec is required.

The phase adjustment unit 802-1, 802-2, the phase synchronization control unit 803, the phase estimation unit 804-1, 804-2, the reception unit 805-1, 805-2, and the signal switching unit 806 are independent devices. It does not have to be a device that handles the optical signal as it is, or it may be a device that converts the optical signal into an electric signal for processing. In particular, when converting to an electric signal for processing, a digital signal processor (DSP: Digital Signal Processor), FPGA (Field-Programmable Gate Array), and ASSP (Application Specific) widely used in long-distance large-capacity communication devices are used. Standard Product) etc. can be selected. The phase estimation function already implemented for communication processing in DSP, FPGA, or the like can be used for each element of the wavelength switching processing unit 800, and the above-mentioned phase synchronization control processing can be compactly realized.

Each element of the wavelength switching processing unit 800 does not have to be arranged in the order and connection relationship shown in FIG. 16 as long as the same function as the phase synchronization procedure described with reference to FIG. 17 can be realized, and all the elements are not necessarily provided. You don't even have to. For example, the DEMUX 801 may be a general demultiplexing means used in a conventional optical communication node for dropping an optical signal and guiding it to, for example, a transponder. The demultiplexing means can be variously configured depending on the number of wavelengths, and the DEMUX 801 can be omitted, or the optical switch and the WSS can be combined. It suffices if two optical signals of λ1 and λ2 before and after wavelength switching can be supplied to two data reception paths.

Further, in the wavelength switching processing unit shown in FIG. 16, the output of DEMUX801 is configured to be connected to two data reception paths, but the phase synchronization procedure of FIG. 17 can be performed simultaneously for different wavelength sets. As described above, it is also possible to configure four data reception paths to simultaneously perform two different wavelength switching operations (λ1 → λ2, λ3 → λ4). Further, the positions of the signal switching unit 806 and the receiving units 805-1 and 805-2 can be exchanged to make one receiving unit. Further, after the wavelength switching processing unit 800 of the receiving end node, not only a transponder but also an arbitrary functional block using a dropped optical signal can be connected. Therefore, the wavelength switching processing unit 800 does not necessarily have to include a receiving unit for decoding information data. Further, since phase adjustment (timing adjustment) can be performed on the symbols and data bits after decoding by the receiving units 805-1 and 805-2, before the phase adjusting units 802-1 and 802-2. Receiving units 805-1 and 805-2 may be provided.

By performing the procedure of flow 1000 in FIG. 17, the two optical signals of λ1 and λ2 are phase-synchronized so that the timings of the information data match, and then the signal switching unit 806 converts the wavelength of λ2. By switching to an optical signal, communication with an optical signal of a new wavelength is achieved. After completing the phase synchronization procedure by the wavelength switching processing unit 800, the optical signal of λ1 before wavelength conversion is displayed in the device such as WSS existing in the section where the optical signal of λ2 is transmitted in the node B600 and the node C700. It becomes unnecessary. The wavelength defragmentation of the entire optical communication system is completed by sequentially executing a block of the optical signal of λ1 and deleting unnecessary optical path settings in the section where the optical signal of λ1 existed.

To summarize the optical communication node configuration of the optical communication system of FIG. 16 and the flow of FIG. 17, in the optical communication node of this embodiment, in order to perform wavelength defragmentation without causing data loss, the following steps are performed. It will be carried out sequentially. The receiving end node is in a state of receiving data information by the optical signal of λ1.
(1) At the wavelength switching node, wavelength conversion is performed on the optical signal of λ1 to generate an optical signal of λ2.
(2) At the receiving end node, the phase estimation unit estimates the phase (timing of information data) of each optical signal of λ1 and λ2.
(3) Based on the information from the phase estimation unit, the phase synchronization control unit performs analysis, and feedback control is performed to the phase adjustment unit so that the respective phases are aligned and the timing of the information data is matched.
(4) At the receiving end node, the receiving path is switched from the optical signal of λ1 to the optical signal of λ2, and the optical signal is supplied to the subsequent functional block.
(5) The optical path related to the optical signal of λ1 before wavelength conversion is deleted.

By linking the optical communication node of this embodiment with the operation of the optical communication node that performs the wavelength defragmentation described in Examples 1 to 5 and the phase synchronization procedure at the receiving end node, wavelength switching without data loss can be performed. realizable.

In the optical communication node of the sixth embodiment, the phase synchronization procedure by the wavelength switching processing unit has been described. In the phase synchronization procedure by the wavelength switching processing unit of the sixth embodiment, the phase synchronization and the phase adjustment of the optical signal can be performed before or after the decoding of the optical signal, and a general configuration is shown. In this embodiment, a more specific configuration using a MIMO equivalent device, which enables more efficient phase synchronization at the receiving end node, will be described.

In the experimental system (FIG. 1) described in Non-Patent Document 2, the two wavelengths are modulated by the same signal, and the maximum ratio is synthesized by an adaptive MIMO (Multi-Input and Multi-Output) equalizer. It is disclosed to realize phase synchronization. More specifically, in the experimental system of Non-Patent Document 2 (FIG. 1), optical signals (channel 1, channel 2) having two wavelengths are decoded by a coherent receiver, and the decoded signals are adaptive MIMO and the like. Connected to the chemical device. In the adaptive MIMO equalizer, the tap coefficients of the two signals are controlled to appropriate values, and the two signals are combined. At this time, if the phases of the two signals are appropriately adjusted, the signal quality is maximized, the original optical signal (channel 1) is stopped after setting the maximum quality state. The optical communication node of this embodiment uses a maximum ratio synthesizer (adaptive MIMO equalizer) as a more specific configuration example. Hereinafter, the differences from the configuration of the sixth embodiment will be mainly described.

FIG. 18 is a diagram showing a configuration of an optical communication system according to a seventh embodiment of the present invention. Also in FIG. 18, the wavelength of the optical signal is switched between the two optical communication nodes 600 and 700 without causing data loss. In the two optical communication nodes B600 and the optical communication node C700 shown in the optical communication system of FIG. 18, information data is transmitted to the node C via the node B as in the sixth embodiment. In this embodiment, the wavelength conversion means described in Examples 1 to 5 is used to generate two optical signals, and the optical signals before and after the wavelength conversion are for demultiplexing the receiving end node C700. It is input to the input port In1 of WSS703-1. The multiplexed light including the two optical signals of wavelengths λ1 and λ2 input to In1 is demultiplexed by the demultiplexing WSS703-1, and the two optical signals are demultiplexed from one of the output ports of the demultiplexing WSS to the path 710. Is received by the transponder.

The optical communication node of this embodiment includes a wavelength switching processing unit 900 on the path to the transponder on the Drop port side. The wavelength switching processing unit 900 realizes wavelength switching without data loss in conjunction with the operation of wavelength defragmentation of the optical communication node shown in Examples 1 to 5. The wavelength switching processing unit 900 includes a wavelength demultiplexing unit (DEMUX) 901 that demultiplexes two optical signals having different wavelengths λ1 and λ2, and at least two systems of data reception that detects and estimates the phase of the optical signals of each wavelength. The path, the maximum ratio synthesizer 907 for synthesizing the optical signals of two wavelengths at the maximum ratio, and the phase synchronization control that acquires the phase information of each wavelength and analyzes the phase adjustment amount required to synchronize each phase. It is composed of a part 903. The data reception path of each system includes coherent detection units 906-1 and 906-2 for performing coherent detection, and phase estimation units 904-1 and 904 for estimating the phase of the optical signal input for each wavelength. It is composed of -2.

The maximum ratio synthesis unit 907 calculates the Q value of the signal when the two optical signals are combined at the maximum ratio. The phase estimation units 904-1 and 904-2 estimate the phases of the two optical signals, and control the filter tap and the like of the maximum ratio synthesis unit 907 so that the Q value becomes the maximum. As the maximum ratio synthesizer 907, for example, an adaptive MIMO equivalent device can be used. In the maximum ratio synthesis unit 907, as the degree of coincidence between the two channels increases, the signal level rises above the noise level, and the Q value of the signal increases. Then, when the phases of the two signals are synchronized and the timings of the information data match, the Q value becomes maximum. Therefore, the phases of the two optical signals having wavelengths λ1 and λ2 can be adjusted by utilizing the equalization function of the maximum ratio synthesizing unit 907. When the optical signal of λ2 is input to the wavelength switching processing unit 900, the maximum ratio synthesizing unit 907 immediately operates so that the Q value at the time of maximum ratio synthesizing becomes the maximum. It is the same as in Example 6 that the two optical signals of λ1 before the wavelength conversion are extinguished after the state of the maximum ratio synthesis is reached. In this embodiment, the optical signals of λ1 and λ2 are converted and decoded into electric signals by the coherent detection units 906-1 and 906-2, and the respective electric signals are converted into electric signals by the maximum ratio synthesis unit 907. It is electrically synthesized. Therefore, as the output of the maximum ratio synthesis unit 907, the decoded electric signal 910 after the logic synthesis is output. Therefore, the switching switch as in the sixth embodiment is unnecessary. Switching to the optical signal of λ2 only needs to quench the optical signal of λ1 while the signal of λ1 and the signal of λ2 are synchronized.

Also in the optical communication node of the seventh embodiment, when the wavelength conversion means 605 converts the wavelength of the optical signal in the wavelength conversion node B600 that performs wavelength defragmentation, the optical signal of λ1 before conversion and the optical signal of λ2 after conversion are used. Can coexist at the same time. By using the adaptive MIMO equalization unit used in communication technology, it is possible to realize a phase synchronization procedure without data loss with the minimum required configuration.

In any of the above-mentioned Examples 6 and 7, each block of the wavelength switching processing units 800 and 900 can be configured in, for example, a transponder corresponding to the wavelength of the optical signal on the Drop side. Further, the phase synchronization control units 803 and 903 can be configured as a part of a common control unit of the transponder, for example.

As described in detail above, the optical communication system of the present invention includes an optical communication node capable of realizing more flexible and simple wavelength defragmentation as compared with the prior art. By linking the wavelength defragmentation operation of the node that performs wavelength conversion with the phase synchronization procedure at the receiving end node, stable operation of the optical communication system becomes possible by wavelength switching without data loss.

The present invention can generally be used in communication systems. In particular, it can be used for an optical communication node of an optical communication system.

11, 12, 13, 20, 400, 500, 600, 700 Optical communication nodes 21-1 to 21-3, 603-1 to 603-3 WSS for demultiplexing
24, 24a to 24i, 605 Wavelength conversion means 25, 25-1 to 25-3, 601 Pump light generation means 25a Excitation light generation unit 25b Frequency shift unit 26 Excitation light selection and distribution unit 27 Drop port 28 Add port 26-1 to 26-3, 401, 501 M × p WSS
29-1 to 29-3 WSS for combined wave
46, 50, 71 EDFA
47 HNLF
48 1 × M WSS
49 SSB modulator 52 M × 1 WSS
53 1 × p WSS
70 Optical confluence 72 Non-linear optical medium 102 Diffraction grating 103, 104 Cylindrical lens 105 Deflection element (LCOS)
800, 900 Wavelength switching processing unit 801, 901 Wavelength demultiplexing unit 803, 903 Phase synchronization control unit 805-1, 805-2 Receiving unit 804-1, 804-2, 904-1, 904-2 Phase estimation unit 906- 1,906-2 Coherent detection unit 907 Maximum ratio synthesis unit

Claims (8)

In an optical communication system that multiplexes optical signals of different wavelengths and transmits information data.
Multiple wavelength division frequency selection switches that demultiplex wavelength division multiplexing signals from different input routes,
A plurality of combined wave wavelength selection switches for combining wavelength division multiplexing signals including demultiplexed signal light from each of the plurality of demultiplexing wavelength selection switches, and
A plurality of paths for interconnecting each of the plurality of demultiplexing wavelength selection switches and each of the plurality of combined wave wavelength selection switches are provided.
A wavelength conversion means is installed for at least one of the paths connected to the plurality of combined wave wavelength selection switches .
The first optical signal before the wavelength conversion by the wavelength conversion means and the second optical signal whose wavelength is converted from the first optical signal are the first optical signal and the second optical signal. During the phase synchronization procedure between
A wavelength demultiplexing means for wavelength-dividing the first optical signal and the second optical signal from the first optical communication node, and
A timing estimation unit that estimates the timing of information data between the first optical signal and the second optical signal, and a timing difference of information data between the first optical signal and the second optical signal. An optical communication system including a wavelength switching processing means including a timing adjusting unit for reducing the number of light signals, and a second optical communication node for dropping the second optical signal carrying the information data. The timing estimation unit coherently detects the first optical signal and the second optical signal, respectively, and performs timing estimation on the two decoded information data.
The claim is characterized in that the timing adjusting unit is a maximum ratio synthesizing unit that adjusts the timing of the two information data so as to maximize the combined output by synthesizing the two information data in the maximum ratio. Item 1. The optical communication system according to Item 1. The at least one path of the first optical communication node is
A claim comprising a path from at least one combination of the demultiplexing wavelength selection switch and the combined wave wavelength selection switch, or a path from an Add port connected to the plurality of combined wave wavelength selection switches. Item 2. The optical communication system according to Item 1 or 2. Further, an excitation light generating means for supplying excitation light to the wavelength conversion means is provided.
The optical communication system according to any one of claims 1 to 3, wherein the wavelength conversion means is an all-optical wavelength conversion means in which wavelength conversion is performed only by an optical layer. The excitation light generating means is
Excitation light generator that generates frequency comb light from CW light,
A comb separation means for spatially demultiplexing the frequency comb light generated in the excitation light generation unit into a single CW light for each comb frequency.
A plurality of frequency shift units that shift the frequency of the single demultiplexed CW light, and
The optical communication according to claim 4, further comprising an excitation light selective distribution means that combines and spatially demultiplexes the frequency-shifted CW light from each of the plurality of frequency shift units. system. The optical communication system according to claim 5, wherein the excitation light selective distribution means is a wavelength selection switch having multiple inputs and multiple outputs. In the optical communication system according to any one of claims 1 to 6.
A step of performing wavelength conversion on the first optical signal of wavelength λ1 and generating the second optical signal of wavelength λ2 at the first optical communication node.
In the second optical communication node, a step of estimating the timing of the first optical signal and the second optical signal by the timing estimation unit, and
A step of operating the timing adjusting unit in the second optical communication node so that the timing difference between the first optical signal and the second optical signal is reduced.
The step of switching the receiving path from the first optical signal to the second optical signal at the second optical communication node and acquiring the information data from the second optical signal.
A method for controlling an optical communication node, which comprises performing a phase synchronization procedure including a step of deleting an optical path related to λ1 at the first optical communication node and the second optical communication node. An optical communication node that drops an optical signal carrying the information data in an optical communication system that multiplexes optical signals of different wavelengths and transmits information data.
From different optical communication node, a first optical signal and, prior SL and a second optical signal the first optical signal is wavelength-converted, wavelength division means for wavelength division before being wavelength converted,
A timing estimation unit that estimates the timing of the information data between the first optical signal and the second optical signal, and the information data between the first optical signal and the second optical signal. A wavelength switching processing means including a timing adjustment unit for reducing a timing difference is provided, and the different nodes are a plurality of demultiplexing wavelength selection switches for demultiplexing wavelength-divided multiplex signals from different input directions, and the plurality of demultiplexing. A plurality of combined wave wavelength selection switches for combining wavelength-divided multiplex signals including demultiplexed signal light from each of the demultiplexing wavelength selection switches, and each of the plurality of demultiplexing wavelength selection switches, and the plurality. For at least one path among the paths connected to the plurality of combined wave wavelength selection switches having a plurality of paths interconnected with each of the combined wave wavelength selection switches. It said first optical signal or found before Symbol second wavelength converter for wavelength-converting the optical signal is disposed, between the phase synchronization procedure between the first optical signal and the second optical signal, The first optical signal and the second optical signal are configured to be simultaneously output from one of the plurality of combined wave wavelength selection switches. Optical communication node.

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